Welcome to the Apple Community.
Click on your account name in the top right corner of the iTunes store in the iTunes application on your computer, enter your password and click the "view account" button. Navigate to the Apple ID summary where you have the option to "change country or region".
In order to change your location, you will need a credit card registered to an address in the location you are trying to change to.
You cannot change your location if you have credit on your account, if you are unable to spend your credit and leave a balance of zero, contact Apple, which you can do through iTunes Store Support.